I stuck a Saito 91 on my Tower 60 trainer for a while (to break in the engine)....it was a blast Now it's sportin' an OS 70FS....ample power, but not nearly as much fun as the 91

This is the Ford vs Chevy thread but, here's my opinion anyway. I've got two TT Pro 46s and two TT Pro 61s one 46 FX one 55 AX one 75 AX and one 91 FX. For the difference in the price I would go with the TT Pro engine. They are just as easy to break in, tune and keep up as the OS engines. Two of the TT Pro engines were my first engines. They have more gallons through them than I care to think. My trainer proably gets more flights on it still than any of the other planes and all I have done to it is one glow plug. It'll crank everytime with a chicken stick. One flip if it's above freezing. Might take two if it's cold. It's a 61. Getting parts for the OS engines has been simple. You can call Tower and they will get them on the way. I don't know how hard it will be to get parts for the TT engines, I've not needed any yet.

i run turbines and da100's don't use the smaller engines any more. had a 91 magnum nothing but trouble with it . it ended up in the bin.had os 46fx.46ax.160fx.91fx bloody good engines only one i will go with if i ever go smaller which i doughbt { sorry about the spelling} fair enough os maybe a bit more money but for reliability they are the best of that i have seen and used

You can send me that trashed Magnum if you need to get rid of it!

It is all well and good to plan to migrate a trainer engine to another plane, but as someone else pointed out most of the 60 size Yaks and similar planes are not being powered by 60 class engines.
They are being powered by Saito 125's.
The Saito weighs in at 24.7 oz and the OS75AX weighs in at 26.46 oz.
So if you really want to migrate the engine from your trainer to your 60 sized Yak you might consider the Saito 125.
Just a thought.